Hard disk drives store large volumes of data on one or more disks mounted on a spindle assembly. Disk drives employ a disk control system for interfacing with a host (e.g., a computer) to control the reading and writing of data on a disk. Each disk includes at least one disk surface that is capable of storing data. On each disk surface, user data is stored in data sectors (i.e., data sites) organized in concentric circular tracks between an outside diameter and an inside diameter of the disk.
As a result of the manufacturing process, defective data sites may exist on the disk surfaces of the disk drive. These defective data sites are conventionally termed “primary” defects. A defect discovery procedure is performed to locate these defects and mark them out as defective locations on the disk surface that are not available for use. A typical defect discovery procedure includes writing a known data pattern to the disk surface and subsequently reading the data pattern from the disk surface. Defective data sites are identified by comparing the data pattern read from the disk surface with the known data pattern written to the disk surface.
Following the defect discovery procedure, defective data sites are written to a primary defect list (PLIST). The primary defect list is used during formatting of the disk surface to generate a primary defect management table. Once identified in the primary defect management table, the defective data site may not be used for storing data and are passed over or “skipped” during disk drive operations. The PLIST, therefore, is used to archive the location addresses of defective data sites discovered after manufacturing but prior to actual use of the drive so that users can retrieve the information at a later time. As an example, the number of data sites residing on the PLIST provides a generalized indication of the state of the media. Entries in the PLIST are stored in a cylinder/head/wedge/position/length format. This allows a single PLIST entry to represent defects of varying lengths (e.g., multi-sector defects).
Defective data sites encountered after formatting the disk surface or during operation of the drive are known as “grown defects”. Grown defects often occur in locations adjacent to defective data sites found during defect discovery. Grown defects are also written to a list, known as the grown defect list (GLIST), similar to that utilized for the primary defects. The GLIST is used to archive the location addresses of defective data sites discovered during normal drive operations so that users can retrieve the information at a later time. Therefore, the number of data sites residing on the GLIST may provide a generalized indication of the health of the drive. GLIST entries are represented in a cylinder/head/wedge/position/length format, where each entry describes a defect of exactly one sector. In contrast to the skip type entries of primary defects, grown defect sites are typically not skipped, but are redirected to alternate data site locations on the disk, which contains the reassigned data of the data site experiencing the grown defect.